We shall investigate the intermediate stages in the in vitro assembly of protein from tobacco mosaic virus. Of specific interest are the details of formation of the nucleus equivalent to about two turns of the virus rod and of the stage requiring the binding of protons. Experimental approaches will involve velocity and equilibrium sedimentation. For the latter, data will be reduced using an original procedure applicable to polymerizing systems. An attempt will be made to devise a system for computer processing of such data. We have separated by sephadex gel filtration fd bacteriophage A protein and are determining the number per virus particle, preliminary to carrying out its biophysical and immunological characterization. In addition, our results on the ion etching of both TMV and T4 bacteriophage suggest that this technique may allow us to determine the location and orientation of the single stranded DNA within fd. Also, we have carried out fluorometric studies on DNA and synthetic polynucleotides stained with quinacrine. We intend to study fluorescent changes brought about by the addition of viruses to acridine dyes and the effect of TMV protein-dye interaction on the polymerization of the protein. BIBLIOGRAPHIC REFERENCES: "Ion Etching of Tobacco Mosaic Virus and T4 Bacteriophage", I. J. Bendet and N. Rizk, Biophys. Journ. 16, 357-365 (1976). "The A Protein of Bacteriophage fd: Its Interference with Viral Infection", T-C. Lin and I.J. Bendet, Biochem. Biophys. Res. Comm. (in press) (1976).